Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.26   9.789%   $267.0727   $267.07   $267.05   $267.10  
  Purchase #2 $223.68   3.248%   $230.9451   $230.95   $230.95   $230.90  
  Purchase #3 $121.71   7.766%   $131.162   $131.16   $131.15   $131.20  
  Purchase #4 $64.25   3.315%   $66.3799   $66.38   $66.40   $66.40  
  Purchase #5 $34.70   3.659%   $35.9697   $35.97   $35.95   $36.00  
  Purchase #6 $227.54   3.737%   $236.0432   $236.04   $236.05   $236.00  
  Purchase #7 $162.90   4.661%   $170.4928   $170.49   $170.50   $170.50  
  7 purchase totals = $1,078.04       $1,138.0654   $1,138.06   $1,138.05   $1,138.10